1. Field of the Invention
The invention relates to the addition of a supplemental air spring and linear guide to a leaf spring suspension system for vehicles and a kit of parts for adapting vehicles after assembly.
2. Description of the Prior Art
Vehicles such as light trucks or sport utility vehicles generally have relatively large suspension travel for use over rough and unimproved surfaces. While such vehicles have found favor among the general public for recreational purposes, they are also widely used by construction firms, the military, and other users as well.
The two most important considerations in the suspension action of such vehicles are total travel or the amount of movement from full compression (“bump”) to full extension (“droop”), and articulation. This total travel is the difference in travel extremes between diagonally opposite wheels or wheel assemblies at diagonally opposite corners of the vehicle. These characteristics are of critical importance in extreme conditions, as obviously a wheel and tire which is not in contact with the underlying surface, is incapable of providing any tractive force (acceleration, braking, and/or steering) to propel and control the vehicle.
As a result, manufacturers and aftermarket suppliers alike have attempted to develop various solutions for these travel and articulation problems. As suspension travel increases in any given vehicle, the problem of providing sufficient articulation becomes more critical. Greater suspension travel results in greater angularity in drive lines and axles relative to one another and to the vehicle frame, creating an even greater problem in avoiding binding somewhere in the system.
This is particularly true in vehicles with solid axle systems, where the suspension elements (springs and shock absorbers) are connected between an axle which extends across the vehicle and the vehicle chassis or frame. A large number of vehicles (particularly older vehicles) have solid axles (perhaps front and back) suspended by leaf springs, as this system has proven to be extremely durable and reliable.
While leaf spring suspensions have a long history of use, leaf spring suspensions are a static or fixed suspension system. Leaf springs are elongated members used as a flexible beam to support the weight of a motor vehicle. In the suspension system of a vehicle, leaf springs provide a simple, cost-effective, and easy to design suspension system. The leaf spring suspension system can provide support without assistance from other structural components acting in parallel to them. Leaf springs provide full support for the suspended structure in vertical directions and can also provide full support for the suspended structure in lateral and longitudinal directions.
The use of only leaf springs in a vehicle's suspension system to support the weight of the suspended structure, however, has disadvantages as compared to the use of other types of springs. Leaf spring assemblies are conventionally formed of a series of separate springs of different lengths, laminated together by a corresponding series of shackles or the like. As the aft ends of the spring are secured to the vehicle by lateral pivot bolts or pins, the aft ends maintain the angular orientation of the vehicle about their lateral pivot axes, while the center of the spring, which is bolted to the axle, is twisted to align with the lateral angle of the axle. This twisting alignment twists the spring assembly, with resulting binding and resistance to spring travel and movement. The twisting alignment also places severe shear forces at the ends of the spring-to-chassis attachment bolts, leading to their early failure. Leaf springs also weigh more than other types of springs with equivalent weight carrying capabilities. Many factors, such as weight carrying requirements, limitations in the length of leaf springs due to space constraints and fatigue strength of the leaf springs, often require that leaf springs have greater spring rates than is necessary for other types of springs. The greater spring rates can result in a harsher ride for the occupants and cargo of the vehicle and reduced life of the suspended structure.
Additionally, many known designs of suspension systems of vehicles include leaf-spring packs with multiple leaf springs stacked upon one another to provide the load carrying ability. One disadvantage of the use of leaf-spring packs is that friction between a leaf spring and the leaf springs positioned above and below causes hysteresis in the reaction of the leaf-spring pack to changing loads. This hysteresis has the same negative consequences for suspension systems as the negative consequences associated with increased spring rates.
Therefore, there is a need for a suspension system that increases spring rates of a leaf spring suspension system while avoiding the harsher ride and reduced life of the suspended structure. There is also a need for an adjustable suspension system that incorporates the advantages of the leaf spring system but is readily adjustable, such as for use with different weights and types of cargo or for hauling a heavy trailer. A further need is an aftermarket kit that can be added to motor vehicles with existing leaf spring suspension systems to increase the effectiveness of the leaf spring suspension system.